An IC socket accepts an IC (herein, IC is defined as the commercially sold product being a packaged chip or die with electrical leads available for making external connections--not the chip or die itself), makes electrical contact with the leads of the IC, and provides electrical connections to the printed circuit board to which the socket is soldered or otherwise attached. Of critical importance to all sockets is the ability to reliably align the IC leads and the socket contacts. This is especially true of sockets for fine pitch surface mounted ICs where there are many narrow IC leads arranged close to each other on each side of the IC package. Such ICs have rows of leads that may extend over one or more inches in length.
Some IC sockets for surface mount ICs align the IC leads to the socket contacts by providing fixed mechanical posts, protrusions or the like that guide and position the IC package within the socket cavity. One such means provides for locator posts for each of the four corners of the IC package. As the IC is fitted into the cavity, the locator posts guide the corners to positions where the IC is in a mechanically controlled, known position so that the IC leads will be aligned with the socket contacts.
Other sockets use mechanical protrusions that form a cavity under the IC package where rails extend upward from the base to accept each of the four underneath edges (as compared to the corners of the previous paragraph) of the IC package. When the IC package is fitted to this cavity the IC package is aligned to the socket at a known location designed to ensure that the IC leads and the socket contacts are aligned.
In both of the above described sockets, the IC package, when the IC is inserted into the socket cavity, conforms to the molded body of the socket. Thus, in both of these configurations the mechanical tolerances of the IC package and the socket are factors that directly affect the alignment quality of the socket/IC combination. As a result, damage to the fragile IC leads may occur. The mechanical tolerance chain is as follows: (1) the IC lead size, (2) the IC lead to the IC package corners and/or edges, (3) the fitting of IC package to the rails or corner posts of the socket, (4) the rails or corner posts to the location of the socket contact locations, and (5) the location of the socket contacts within the contact locations. This chain of tolerances must be controlled and maintained to tight dimensions--the lack of such control will contribute to socket failure and unreliability.
An object of this invention is to provide an IC socket system with improved alignment of the IC leads to the socket contacts.
It is another object of this invention to reduce the damage to IC packages when used with a socket.